1. Field of the Invention
The present invention relates to a heat exchanger, and more particularly, to a method of assembling and the construction of a heat exchanger for use as an evaporator or a condenser.
2. Description of the Prior Art
With reference to FIG. 1, a conventional refrigerant circuit for use, for example, in an automotive air-conditioning system is shown. Circuit 1 includes compressor 10, condenser 20, receiver or accumulator 30, expansion device 40, and evaporator 50 connected through pipe members 60 which link, the outlet of one component with the inlet of a successive component. The outlet of evaporator 50 is linked to the inlet of compressor 10 through pipe member 60 so as to complete the circuit. The links of pipe members 60 to each component of circuit 1 are made such that the circuit is hermetically sealed.
In operation of circuit 1, refrigerant gas is drawn from the outlet of evaporator 50 and flows through the inlet of compressor 10, and is compressed and discharged to condenser 20. The compressed refrigerant gas in condenser 20 radiates heat to an external fluid flowing through condenser 20, for example, atmospheric air, and condenses to the liquid state. The liquid refrigerant then flows to receiver 30 and is accumulated therein. The refrigerant in receiver 30 flows to expansion device 40, for example, a thermostatic expansion valve, where the pressure of the liquid refrigerant is reduced. The reduced pressure liquid refrigerant flows through evaporator 50, and is vaporized by absorbing heat from a fluid flowing through the evaporator, for example, atmospheric air. The gaseous refrigerant then flows from evaporator 50 back to the inlet of compressor 10 for further compression and recirculation through circuit 1.
With further reference to FIGS. 2 and 3, there is shown a prior art embodiment of condenser 20 as disclosed in Japanese Utility Model Laid-Open SHO 63-49193. Condenser 20 includes a plurality of adjacent, essentially flat tubes 21 having an oval cross-section and open ends which allow refrigerant fluid to flow therethrough. A plurality of corrugated fin units 22 are disposed between adjacent flat tubes 21. Circular header pipes 23 and 24 are disposed perpendicularly to flat tubes 21 and may have, for example, a clad construction. Header pipes 23 and 24 have slits 25 disposed therethrough. Flat tubes 21 are fixedly connected to header pipes 23 and 24, and are disposed in slits 25 such that the open ends of flat tubes 21 communicate with the hollow interior of header pipes 23 and 24.
Header pipe 23 has an open top end and an open bottom end. The open top end and the open bottom end are respectively sealed by inlet union joint 23a and outlet union joint 23b which are fixedly and hermetically connected thereto. Inlet union joint 23a is linked to the outlet of compressor 10. Outlet union joint 23b is linked to the inlet of receiver 30. Partition walls 23c are fixedly disposed within and divide header pipe 23 into upper chamber 231, middle chamber 232 an lower chamber 233. Header pipe 24 has a closed top end and a closed bottom end. Partition wall 24a is fixedly disposed within header pipe 24 at a location about midway along its length and divides header pipe 24 into upper chamber 241 and lower chamber 242 which is isolated from upper chamber 241. The location of partition wall 24a is lower than the location of upper partition wall 23c and is higher than the location of lower partition wall 23c.
In operation, compressed refrigerant gas from compressor 10 flows into upper chamber 231 of header pipe 23 through inlet union joint 23a, and is distributed such that a portion of the gas flows through each of flat tubes 21 which are disposed above the upper partition wall 23c. The gas in flat tubes 21 then flows into an upper portion of upper chamber 241. The refrigerant in the upper portion of upper chamber 241 then flows downward into a lower portion of upper chamber 241, and is distributed such that a portion flows through each of the plurality of flat tubes 21 disposed below the location of upper partition wall 23c and above the location of partition wall 24a. Then, the gas flows through flat tubes 21 into upper portion of middle chamber 232 of header pipe 23. The refrigerant in an upper portion of middle chamber 232 flows downward into a lower portion thereof, and is distributed such that a portion flows through each of the plurality of flat tubes 21 disposed below the location of partition wall 24a and above the location of lower partition wall 23c. Then, the gas flows into the upper portion of lower chamber 242 of header pipe 24. The, refrigerant in an upper portion of lower chamber 242 flows downward into a lower portion thereof, and is distributed such that a portion flows through each of the plurality of flat tubes 21 disposed below the location of lower partition wall 23c, and into lower chamber 233 of header pipe 23.
As the refrigerant gas sequentially flows through flat tubes 21, heat from the refrigerant gas is exchanged with the atmospheric air flowing through corrugated fin units 22. Since the refrigerant gas radiates heat to the outside air, it condenses to the liquid state as it travels through tube 21. The condensed liquid refrigerant in lower chamber 233 flows out therefrom through outlet union joint 23b and into receiver 30.
As shown in FIG. 3, header pipe 23 includes slit 26 formed opposite slits 25. Slit 26 is formed between two adjacent slits 25. Partition plate 27 forming a partition wall 23c within header pipe 23 includes small diameter semicircular portion 271 and larger diameter semicircular portion 272 integrally formed such that two semicircular portions are joined at their chordal surfaces. Portion 271 has a diameter substantially equal to the inner diameter of header pipe 23 and portion 272 has a diameter substantially equal to the outer diameter of header pipe 23. Partition plate 27 is disposed in slit 26 such that portion 271 fits flush against the inner surface of header pipe 23 and the outer surface of portion 272 is disposed such that the end portions 272a of portion 272 fit flush against the end portions 262 of slit 26. Accordingly, after assembly, partition plate 27 cannot move toward the inside of header pipe 23 and is substantially even with the outer surface of header pipe 23.
More particularly, after assembly, the heat exchanger, which is held together by various jigs, is placed into, a brazing kiln. Ideally, the jigs maintain the various parts of the heat exchanger in their relative positions until the brazing process permanently sets the parts. While partition plate 27 is prevented from moving toward the inside of header pipe 23 by the engagement of end portions 272a, 262, there is nothing preventing the partition plate 27 from sliding outside of slit 26 once placed therein. Moreover, there is a clearance between the top and bottom of the partition plate 27 and the periphery 261 of slit 26. Consequently, partition plate 27 can assume various angles with respect to the longitudinal axis of header pipe 23.
With reference to FIGS. 4 and 5, the inside of header pipe 23 is made of aluminum metal 23d and the outside of header pipe 23 is made of an alloy of aluminum and silicon 23e layered on the circumference of aluminum metal 23d. The melting point of the alloy is lower than the melting point of aluminum metal 23d. Consequently, the alloy of aluminum and silicon 23e brazes partition plate 27 with header pipe 23.
Since partition plate 27 is not secured once placed inside slit 26, the position of the plate 27, although correct upon initial insertion, can easily be altered by a slight vibration or shock during, for example, transporting the heat exchanger to the brazing kiln. Once the heat exchanger is heated in the kiln, any misalignment of the partition plate 27 creates permanent defects in the heat exchanger construction. For example, end portions 272a, 262 may not be completely flush. In this case, the partition plate 27 would be brazed to the header pipe 23 such that a space is created between portion 271 and the inner surface of header pipe, thereby allowing some of the refrigerant to bypass the multiple passes through the heat exchanger. Alternatively, the partition plates 27 might be angled to such a degree in the slits 26 that the braze between the slit 26 and the partition plate 27 is too thin to last the entire service life of the heat exchanger. In this case, the header pipe, proximate to the partition plate 27, could likely spring a leak through which refrigerant flows to the atmosphere.